Wave generator



E. R. MCCOPPIN Oct. 6, 1953 WAVE: GENERATOR Original FiledNov. 7, 1945/mm mmm m W .O mcs m VR mw E R E V E ABY 0 QUZDF Dux-u) Patented Oct. 6,1953 WAVE GENERATOR Everett R. Mccoppin, Dayton, omo

Original application November 7, 1945,` Serial No. 627,273. Divided andthis application July 27, 1949, Serial No. 107,132

(Cl. Z50-36) (Granted under Title 35, U. S. Code (1952), sec. 266) 8Claims.

The invention described herein may be manufactured and used by or forthe Government for governmental purposes, Without the payment to me ofany royalty thereon.

This application is a division of application Serial Number 627,273,filed November 7, 1945, issued October 25, 1949, as Patent No.2,485,620.

The present invention relates generally to Wave form generators, and ismore particularly directed to a sweep-voltage generator adapted to theproduction of a sweep-Voltage Whose value varies directly with thecapacitance of a variable capacitor, for use with a panoramicradio-frequency receiver or spectrosccpe.

Noise disturbances induced in an antenna and received signals as well,are normally distributed over a considerable frequency band. According-1y, apparatus intended for measurement and examination of such receivedsignals or impulses must be designed to record or present theirfrequency as well as their amplitude Within a selected portion of theradio spectrum. It is frequently desirable in such apparatus to halt'the scanning and sweep at a. given frequency in order to 'obtain animproved presentation at that point, but with apparatus heretofore knownin the art, neither such an action nor any but a substantially linearsweep is possible.

Accordingly, it is the main object of this invention to provide a novelsweep-voltage generator which can be stopped at any point 'in its sweepand will thereupon continuously maintain the voltage at that point.

Another object of this invention is to provide a sweep-voltage generatorwhich produces a sweepvoltage and is capable of maintaining a steadyvoltage of any desired value Within said sweepvoltage range.

It is still another object of this invention to provide a new andimproved sweep circuit for use in apparatus designed for noise or signalmeasurement, which will permit the examination of inputs at any givenfrequency within a given band, and will in scanning and display followany desired law of frequency variation.

A further object of this invention is to provide a new and improvedinstrument for noise or signal measurement arranged to displaysimultaneously the amplitude and frequency of all signals and noiseenergy within a predetermined band.

For a complete understanding of the invenf tion, as well as otherobjects and features thereof, reference is made to the followingdetailed description to be read in connection with the ac- 2 'companyingdrawing, depicting in a functional block diagram partially in schematicform, one preferred embodiment of a spectroscope in accordance with theinvention. The scope of the invention will be pointed out and defined inthe accompanying claims.

The spectrosccpe as shown in the drawing mainly comprises an untunedradio-frequency amplifier I0, a converter stage I-I, a variablehigh-frequency oscillator I2, a radio receiver I3, an audio-frequencyrectifier I4, a cathode-ray oscilloscope I 5, and a sweep-voltagegenerator I Ii.

In general terms the behavior of the spectroscope is as follows: Noiseimpulses are intercepted by 'a pick-up loop I'I or any other suitableradiofrequency probe and are heterodyned in converter II with signalsVfrom oscillator I2 which are frequency modulated within a prescribedband. Re-

. ceiv'er I3 is resonant at a fixed frequency and is associated with theoutput circuit of converter I I whereby in the course of a completetuning cycle of variable oscillator I2, a beat radio frequenc'y equal tothe Vresonant; frequency of receiver I3 is derived 'from the output ofconverter I I, the amplitude of said beat being proportional to thelevel of that noise impulse producing said beat. Thereupon the beatfrequency is translated into an audio-frequency of proportionalamplitude by receiver I3 and is then rectified by audioyfrequencyrectier I4 whose direct-current output potential corresponds inmagnitude to the input audio-frequency amplitude.

The `direct-current output of rectifier I4 is applied to the verticallydeflecting means of cathode-ray oscilloscope I5, thereby deiiecting thecathode-raybeam in a vertical direction above the base line to an extentin accordance with the amplitude of the beat frequency. Sweep-Voltagegenerator I6 provides a sawtooth voltage which var-ies in synchronismwith the frequency scan of oscillator I2, said sawtooth voltage beingimpressed on the horizontal deflecting means of oscilloscope I5.

Accordingly, as the cathode-ray beam is deected vertically to an amountin accordance with the noise impulses, the beam is concurrently swepthorizontally in accordance with the position of the noise impulsefrequency in the band. Thus, there is presented on the screen ofoscilloscope I5 a panoramic View of the noise impulses within apredetermined band. By Calibrating the horizontal screen base in termsof frequency and the vertical base in terms of amplitude, aninstantaneous measurement of these noise impulses is given.

Features of the present invention will become more evident in thefollowing explanation of the schematic circuits of converter II,variable frequency oscillator I2, and sweep-voltage generator IE.

By way of example, let it be assumed that noise impulses lying within aband of .1 to 4 megacycles are to be analyzed and that this noise bandis present in the output of untuned amplifier I 0.

Variable frequency oscillator I2 is tunable within a range between 12.1and 16 megacycles. Thus as oscillator i2 scans, a 12 megacyclesdifference beat is produced in the output circuit of converter IIsequentially for every noise impulse within the noise band beinganalyzed, the other beats being discriminated against by the circuitarrangement. It is to be noted that at any instant a specific frequencyof oscillator I2 is heterodyned with all frequencies in the noise band.In the course of a tuning cycle of oscillator I2, the difference beatcommon to al1 frequency combinations in this instance is l2 megacycles.

Receiver I3 which is of standard construction, preferably asuperheterodyne having a high order of sensitivity and selectivity, isfixed at 12 megacycles. Conventional oscillator means are incorporatedtherein for beating with the received radio-frequency signal to producean audio-frequency tone.

Converter II is a standard circuit except that the input circuitsthereof are untuned to provide a broad band characteristic. It includesa pentagrid vacuum tube I8 having the control grid thereof coupled tothe output of untuned amplifier II) through a xed capacitor I 9. Theplate circuit of tube I8 includes a parallel-resonant network 20 peakedat l2 megacycles, said network being adapted to reject all otherfrequencies. Y

Variable frequency oscillator I2 is of conventional design and includesa triode 2I associated with a resonant circuit having an inductance 22shunted by a variable capacitor 23. The signal generated by oscillatorI2 is impressed on the injector grid of converter tube I 8 throughcoupling capacitor 24. Capacitor 23 is of balanced construction, beingvariable through 360 degrees of rotation and attaining maximum capacityevery 90 degrees in the course of rotation. Consequently, the frequencyrange of oscillator I2 is fully traversed in one direction during -90and 18T-270 in a rotation cycle and in the reverse direction during90-180 and 270-360.

Sweep-voltage generator I6 includes a vacuum tube 25 incorporating atriode and diode section. The triode elements of tube 25 are associatedwith a fixed parallel-resonant network 26 in a conventional Hartleyoscillator arrangement. In.. ductively coupled to network 25 is a coil2l, one side thereof being connected to the diode plate of tube 25, theother side being grounded through fixed capacitor 28. Thus the R.F.voltage across coil 2l is rectified by the diode, the resultantpulsating direct-current being filtered by capacitor 28 and a resistor3|. The output of generator IB is obtained at terminals 30.

Connected between parallel-resonant network 26 and coil 2l, at therespective plate and cathode connections to .the triode section of tube25, is a variable capacitor 29, of a construction design similar tocapacitor 23 of variable oscillator I2. It will now be observed thatcoil 21 is capacitatively coupled to network 26 by variable capacitor 29and also, by reason of its proximity, inductively coupled thereto. Thephase of voltage induced inductively in coil 21 is in phase oppositionto that applied capacitatively by variable capacitor 29, hence ascapacitor 29 is increased in value the rectified voltage acrossterminals 3B correspondingly diminishes as the capacitative transferapproaches the inductive transfer. The arrangement is made such that thecapacitative transfer never exceeds the inductive transfer.

Since capacitor 29 is similar to capacitor 23 it undergoes a full changein value four times each cycle of rotation.

In the present embodiment variable capacitors 23 and 29 are preferablyof the type having a linear characteristic. Consequently, when capacitor29 is rotated continuously, the voltage appearing across terminals 30assumes the uniform sawtooth form illustrated by wave pattern 3l.

It is to be noted that the operating frequency of the Hartley'oscillatorin sweep-voltage generator I6 is not significant and does not controlthe frequency of sawtooth wave 3l. The frequency of sawtooth wave 3I is,however, governed by the rate of rotation of capacitor 29, saidcapacitor being driven by a motor 32 whose shaft is also mechanicallyganged to capacitor 23.

The ganged arrangement of capacitors 23 and 29 is such that sawtooth 3icommences at one end of the frequency range of oscillator I2 andsynchronously attains maximum voltage at the other end of the range,whereupon as the range is traversed in the opposite direction, thesweepvoltage falls to minimum.

Terminals 3B are connected to the horizontally deflecting plates ofoscilloscope I5, while the output of audio-frequency rectier I4 isconnected to the vertically deflecting plates thereof. As a result, inthe course of the full concurrent rotation of capacitors 23 and 29, thecathode-ray beam is swept across the screen in one direction therebydisplaying all noise impulses within the prescribed band determined byoscillator I2, and the beam then retraces the same band in the reversedirection.

There exists a distinct advantage in this method. Inasmuch as theluminosity of the trace is an inverse function of beam velocityytheslower the scanning process the more visible is the presentation.However, in order to obtain visual persistence scanning speed above apredetermined minimum must be attained. Therefore, by utilizing both theforward and return portions of the trace in the manner of the presentinvention, it is possible to reduce beam velocity with f out sacrificingvisual persistence.

A feature of the invention resides in the ability of the device to dwellon a selected noise impulse or signal, thereby enabling an individualexamination of the impulse. With conventional sweepvoltage generators,after the sawtcoth circuit is triggered the wave runs its course and itis not possible to freeze the resultant voltage wave at any particularlevel in magnitude. In the present invention, however, sweep-voltagegenerator I6 may be maintained at any selected point in the Voltage waveby bringing capacitor 29 to an immediate stop. In consequence, capacitor23, which simultaneously is brought to a halt in a correspondingposi-tion, fixes the frequency of oscillator I2 so that only one noiseimpulse is displayed on the screen of oscilloscope I5. This isaccomplished by means of a brake mechanism 33 of any suitable designworking in conjunction with motor 22.

While the above described embodiment of the invention is shown asemploying capacitors 23 and 29 having a linear characteristic,capacitors having non-linear characteristics of any desired form may besubstituted therefor for the purpose of expanding on the screen ofoscilloscope i5 a desired portion of the frequency range and contracting a portion of lesser interest.

Superposed over the screen of oscilloscope l5 is a grid scale 34 whosehorizontal base line is graduated in terms of frequency and Whosevertical base line is graduated in amplitude. In the present embodiment,grid scale 34 is of linear design but obviously where a non-linearpanoramic system is employed the scale may be correspondingly arranged.

The use of a heterodyne system in the present invention by means ofconverter Il and variable oscillator I2 enables a Wider noise bandcoverage than is possible where the band to be analyzed is determinedonly by the tuning range of receiver I 3.

It is, of course, evident that the present invention may be utilizedwith equal eiectiveness for the analysis of continuous wave signals.

An important advantage of the present invention is that it frees anoperator to investigate an undesired source of noise impulses andpresents instantaneously the results of any noise suppression means hemay introduce at said source.

While there has been shown what is at present considered a preferredembodiment of the invention, it is apparent that many changes andmodiflcations may be made therein without departing from the invention,and it is, therefore, intended in the accompanying claims to cover allsuch changes and modications as fall Within the true spirit and scope ofthe invention.

What is claimed is:

1. A sweep-voltage generator comprising a single source of alternatingcurrent, an impedance, means for deriving two alternating voltages fromsaid single source, means for applying said two voltages in phaseopposition across said impedance, means for rectifying the resultantvoltage across said impedance, and means for periodically varying theamplitude of one of said alternating voltages to vary the resultantvoltage across said impedance, whereby a sweepvoltage is produced in theoutput of said rectifying means.

2. A sweep-voltage generator as set forth in claim 1, wherein saidperiodically varying means is rotatable and varies said sweep-voltagefrom minimum to maximum and then back to minimum a plurality of times ina single rotation.

3. A sweep-voltage generator comprising an oscillator having a tankinductance, a pick-up inductance inductively coupled to said tankinductance, means coupling said tank inductance to said pick-upinductance to develop a voltage thereacross in phase opposition to thevoltage developed by inductive coupling, means for rectifying theresultant voltage across said pick-up inductance, and means forcontinuously varying one of said voltages in phase opposition whereby asweep-voltage is produced inthe output of said rectifying means.

4. A sweep-voltage generator as set forth in claim 3, wherein saidcontinuously varying means is rotatable and varies said sweep-voltagefrom minimum to maximum and then back to minimum a plurality of times ina single rotation.

5. A sweep-voltage generator comprising a radio-frequency oscillatorhaving a tank irrductance, a pick-up inductance inductively coupled tosaid tank inductance, a variable capacitor capacitatively coupling saidtank inductance to said pick-up inductance to develop a voltagethereacross in phase opposition to that developed by inductive coupling,means for rectifying the resultant voltage across said pick-upinductance, and means for continuously varying said capacitor whereby asweep-voltage is produced in the output of said rectifying means.

6. A sweep-voltage generator as set forth in claim 5, wherein saidvariable capacitor is rotatable and its capacitance varies from minimumto maximum and then back to minimum a plurality of times in a singlerotation.

'7. A sweep-voltage generator comprising a radio-frequency oscillatorhaving a tank inductance, a pick-up inductance inductively coupled tosaid tank inductance, a variable capacitor capacitatively coupling saidtank inductance to said pick-up inductance to develop a voltagethereacross in phase opposition to that developed by inductive coupling,means for rectifying the resultant voltage across said pickupinductance, means for continuously varying said capacitor whereby asweep-voltage is produced in the output of said rectifying means, andmeans for stopping the movement of said capacitor whereby saidsweep-voltage is maintained at a selected point.

8. A sweep-voltage generator as set forth in claim 7, wherein saidvariable capacitor is rotatable and its capacitance varies from minimumto maximum at a given rate and then back to minimum at substantially thesame rate a plurality of times in a single rotation.

EVERET'I R. MCC'OPPIN.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,994,232 Schuck, Jr. Mar. 12, 1935 2,405,073 Troell July 30,1946 2,497,883 Harris, Jr. Feb. 21, 1950 2,499,001 Green r-- Feb. 28,1950

